The present invention relates to new and improved formaldehyde and isocyanate-free room temperature, low temperature, heat and IR radiation curable compositions for use as coatings for wood, metal, plastics, ceramic, concrete, and other substrates. The coatings can be used, for example, for kitchen cabinets, automobiles, appliances, wood flooring, and several other applications.
It is well known that exposure to formaldehyde and isocyanate has significant health hazard issues. For example, under a court order OSHA has established long term (8 hours) and short term (15 minutes) PELs (permissible exposure limits) for formaldehyde. The rules require that any company marketing products that release free formaldehyde must label the containers and provide an MSDS showing how much formaldehyde is present. As formaldehyde has been declared a carcinogen, it is regulated as such. Isocyanate-containing coatings, on the other hand, require special breathing equipment for use to avoid respiratory system problems.
In the coatings industry, formaldehyde-containing polymers are commonly used as “crosslinking” resins that react with carboxyl or hydroxyl functional polymers such as polyesters or alkyd resins. Most of the current industrial finishes that require baking use coatings that contain some free formaldehyde. During the spraying process, workers can be exposed to some unsafe levels of free formaldehyde that comes from the paint. The coatings are then baked at temperatures >275° F. forming fully-crosslinked film. After the baking process, there is no longer any significant emission of free formaldehyde.
In the particular case of the wood finishing industry, it is not possible to bake the finishes at high temperature, and therefore a high level of acid catalyst is used to facilitate the crosslinking at room temperature. This type of coating is commonly termed a “conversion varnish”. Typically, a conversion varnish creates a two stage release of free formaldehyde; namely, in the first stage, free formaldehyde is released from the coating itself during spraying and in a second stage, formaldehyde is released during the curing process. This second stage can last for several weeks. Many of these types of coatings are used by manufacturers in finishing kitchen cabinets, and for other indoor wood finishes.
Thus, it would be desirable to eliminate emission of free formaldehyde without compromising performance. In spite of the concerns, the performance and cost effectiveness of these types of coatings make it difficult to replace them. As regulations continue to be more stringent, it is anticipated that elimination of formaldehyde emission will become mandatory.
Additionally, numerous high performance, high solids coating compositions are based upon polymeric systems comprised of either polyester-based or polyacrylic-based polyols and crosslinking agents therefor. These coatings are generally supplied as “one-pack” or “two-pack” systems. In a typical one-pack system, all of the coating ingredients are combined into one storage stable mixture. In a typical two-pack system, a crosslinking agent is combined shortly before application with curing being conducted at ambient or elevated temperatures. Generally, two-pack systems have the advantages of corrosion and humidity resistance, short dry times and tough film thickness. However, two-pack systems utilizing isocyanate crosslinkers or strong acid based crosslinkers have a number of disadvantages; for example, these two-pack systems require special handling and storage operations to avoid human exposure to the toxic isocyanates and acids. Further, the components of two-pack systems can only be mixed shortly prior to use. One-pack systems known in the art typically utilize resins which are susceptible to hydrolysis, which compromise the quality of the coating. Thus, it would be desirable to provide a one-pack, high solids, isocyanate-free system that has the desirable properties of the two-pack systems.
Accordingly, it is an object of the present invention to provide room temperature or low temperature curable compositions which exhibit high performance characteristics such as corrosion and humidity resistance, tough film properties, and no formaldehyde evolution upon curing. It is another object of this invention to provide coating compositions comprising these room temperature or low temperature curable compositions. The compositions of this invention can be cured effectively at lower temperatures without the use of toxic crosslinking agents, and do not liberate formaldehyde on curing. It is also an object of this invention to provide a one-pack, high solids, isocyanate-free system that has the desirable properties of a two-pack isocyanate system.